The testing of coins by electrical means has become increasingly important with the increased use of vending machines. In broad terms these devices seek to separate genuine coins from counterfeit coins. To constitute an economic threat to the vending machine, the counterfeit must cost less than the genuine coin it replaces.
Economic threats to vending machines would seem to be limited to simple counterfeits as metal washers or low denomination foreign coins of similar size and shape which can be economically obtained. The testing devices to fill these needs are relatively crude as suits their task.
Another purpose of coin testing is found in needs of those who purchase bullion coins. In this case a substantial economic threat is posed by a counterfeiter who fabricates a gold exterior resembling a coin on a base metal disk. No collector would physically probe in the inner structure of the coin since in so doing he would destroy much of its numismatic value. Precise electrical methods are of value, since they provide data on the core material by a nondestructive test.